Upsilon the DemonSlayer
by goddess of trix
Summary: TBBT/Charmed/DW: Two demons want to kill Sheldon.  "Why?" you ask.  Sheldon isn't Sheldon.  Sheldon has a fob watch.  And to top it all off, he hasn't much memory of his life before.  Oh look!  A blue box!  Yay!  Watch for angels.  Don't blink.
1. Prologue

I've been reading awesome Doctor Who/TBBT crossover fiction and it inspired me to make one of my own. I started working on this two years ago and hardly got anywhere with it because I couldn't think of motives or anything for anybody. This was originally going to be crossed over with Jumper and it just didn't fit. I switched Jumper out with Doctor Who and everything seemingly fell into place. I hope you enjoy.

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><p>Just a run-down on what's up here: Christie was not Billie's sister. She was instead her cousin. Billie's parents in Charmed were, instead, her aunt and uncle. Billie and Penny are twin sisters. When Billie and Penny's parents discovered that Billie was a witch, they sent her to live in Christie's parents. Christie's mom was a witch as was her dad. Billie' and Penny's mom was Christie's mom's sister.<p>

It's late, I'm tired, and hopefully this does not come across as babble-speak. Good night.

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><p>Prologue<p>

Phoebe's hand brushed Billie's as they both turned a page in the Book of Shadows. Phoebe had been reminiscing with Billie, telling her what had happened over the seven years that she had been a witch. Phoebe gasped and quickly retracted her hand as if she had been burned.

"What? What is it?" asked Billie in a panic.

"I just had a premonition," she said, her eyes still closed. Phoebe opened her eyes and looked at Billie. Although, it was more like she was looking through the girl. "You were there," she said slowly, her eyes focusing on Billie, giving her an odd look.

Billie gave Phoebe a weird look. "Are you okay?" she asked. "Because that could not have been me. I don't plan on leaving you guys and if I do happen to move out of here, I'll still be living in the Bay Area."

"It was just so weird. You were in an apartment with four guys. I think you were eating Chinese food. Three of the guys were sitting on a red couch. The fourth was sitting on a chair and you were sitting on a couch. There was a guy on the end of the couch who was complaining about his food not being prepared properly. He was tall and looked kind of like a preying mantis. All of a sudden two girls fell through the ceiling of the apartment. One girl broke his neck while the other set the room on fire by breathing fire through her mouth."

Billie gasped. "Oh no!"

"What? What is it? What's wrong? Do you know the people I'm talking about?"

Billie's knees buckled under her. Before she collapsed, Phoebe helped her to the ground. Billie looked terrified and pale, her mouth open slightly. "Phoebe, if I tell you something, you have to promise you won't freak out on me."

Phoebe looked at Billie with concern but nodded anyway.

"I have a twin sister. Her name is Penny. And I believe that is who you just saw in your vision. Christie was my cousin, not my sister. And I was living with my aunt and uncle. My parents live in Omaha, Nebraska with my twin sister Penny. I was kicked out of the house because my parents knew I was a witch. My mom's sister, my aunt, was a witch too." Billie pulled her cell phone out of her pocket. "Now if you will excuse me, I have to call my sister and let her know what's up."


	2. Chapter 1

Chapter 1

Penny was sitting on the couch in between Raj and Sheldon when her phone started to ring. She pulled it out of her pocket and checked the caller ID. "Billie?" she questioned. Penny stood up. "Excuse me guys. I'm gonna take this out into the hall." She walked over and opened the door, stepping out into the hall, quietly shutting the door behind her. She opened her phone. "Hello? Billie?"

Billie let out a relieved breath. "Oh Penny. Thank God you answered."

Penny felt a bit confused. "Why wouldn't I? You're my sister. I know we don't talk much, but if there's something wrong, you can tell me. Or if you just need somebody to talk to."

"Remember at Christie's funeral, how we talked and caught up on stuff?"

"Yeah," Penny answered slowly. "Is that what this is about? I don't care that you're a witch. That sounds like it would be kick ass actually."

"It is," said Billie absently. "Well, it has it's pros and cons. But everything does." She made a noise of annoyance. "But that's not why I called. Has anybody moved into your complex recently—like in the past week?"

"I don't think so." Penny went through a mental list of all the reasons Sheldon freaked out in the past week. "Nope." None of them had to do with a new neighbor moving in anywhere in the building. "Why do you ask?" she asked as an afterthought.

"Remember me telling you about the people I live with?"

Penny nodded. "Yeah," she answered into the phone. "The magic witches or whatever."

"The Charmed Ones, the Power of Three."

"Yeah, them."

"They each have an individual power and one of them just had a vision." She went on to tell Penny what Phoebe told her.

By the time Billie had finished the story, Penny was back in her apartment, sitting on the couch, face pale as could be.

"Do you know who I'm talking about?"

"She described him as a preying mantis?" Penny asked slowly. She felt sick to her stomach. Why would anybody want to kill Sheldon? Yes, he was annoying and very blunt all the time, and, albeit, she had moments where she wanted to kill him herself, that didn't mean she would. Besides, for what reason would a demon—or perhaps two of them—want to kill him?

"Yeah," Billie replied back in a quiet manner.

"Oh God, I think I'm gonna be sick."

"The good thing about premonitions though, is that they can be stopped. If you know how to stop them, they won't come true. Their outcome can be changed."

"Oh, wonderful," muttered Penny sarcastically. "Do you know why they might want him dead?" she asked.

"I don't know. In premonitions, motives aren't usually seen."

"Thanks for the heads up sis. What did you say he was eating?"

"He wasn't. He was complaining about his order. It was Chinese food."

"Oh good. That means I have to be prepared for a Friday. I have some time."

"I'm sorry. What?"

Penny laughed. "Sheldon—the preying mantis—is very particular about things and everything—including his meals—has a set schedule. Friday night is Chinese Food Night, as well as Vintage Video Game Night. I made French toast for him and his roommate on a Monday morning once and he threw it out."

Billie snorted into the phone. "Why was that?" she asked, laughing.

Penny smiled. "Because Monday morning is always Oatmeal Day. That was before I knew his schedule. Now I call him Doctor Whack-a-Doodle."

"He sounds slightly insane."

"Oh no. He's not insane. His mother had him tested."

Billie laughed loudly. "He sounds like a riot."

"He's something alright. He also doesn't believe in witchcraft or astrology or magic or anything that can't be explained by science. So this is gonna be difficult to tell him about." She paused as a thought hit her. "_Can_ I tell him? Or is that against some magical protocol or something?"

"Keep an eye on him. If something out of the ordinary happens, like he displays some type of magic power, or you save him from the fire-breathing demon, then tell him. We don't need him freaking out or sending us to the authorities. We've already had a lot of close calls as it is."

Penny gave a sharp nod. "Right. Thanks for letting me know. And I'll keep you updated on what's going on." Penny closed her phone, ending the conversation. "Why would demons want to kill Sheldon?" she asked herself.

Penny didn't know what to do. Did she drop the bomb on Sheldon or did she just keep an eye on him? What if he got in the way and that's why he was killed? But Billie said the demons dropped through the ceiling, set the room on fire and killed Sheldon. Unprovoked. "But why?" she whispered to herself as she stood up. She re-pocketed her phone and walked back across the hall. She absent-mindedly opened up the door and sat in Sheldon's spot.

Sheldon, who had been over at the fridge getting something to drink, walked back over to the couch and cleared his throat.

Penny looked up at him. "Oh right. Sorry." She moved over without a word.

Leonard and Howard both looked at her, stunned. It was a thing between her and Sheldon that whenever she would sit in his spot she would make a comment that would upset him for the next hour or so.

"Penny, are you okay?" asked Sheldon. Even he had noticed her lack of fight.

"What? Oh no, I'm fine."

"No you're not. You didn't even make a biting comment on me be crazy or a whack-a-doodle or insane."

"It's nothing, really. I just got a call from my twin sister that was just a bit disconcerting is all. Really, it's nothing."

"It's not nothing Penny. Whatever is bothering you is clearly upsetting you."

Raj, Howard, and Leonard were carefully watching this interaction between Sheldon and Penny.

"What's happening?" asked Leonard in an undertone.

"It _is_ nothing, Sheldon. Just leave it alone." Penny couldn't even look at Sheldon. She felt guilty. What if _she_ was the reason he got killed. She knew it was nonsense for her to be feeling guilty over this. It wasn't even her fault.

"Do you want to talk about it?"

"No, Sheldon! I do not want to talk about it. God!"

Sheldon let out a sigh of relief. "Oh thank God. Because I really didn't want to talk about it."

"There's the Sheldon I know," said Leonard, no longer confused. He looked at Penny. "I didn't know you had a twin sister, Penny."

"Yeah, her name's Billie. She used to live in Omaha with my parents and I but she was sent to live with our aunt and uncle and our cousin Christie when we were ten. I don't really want to talk about it." _Because then we'd be encroaching on personal details._

Penny ate in silence while the boys did what they normally did on Mondays. She set her container down on the coffee table and leaned back on the couch. She stole silent glances at Sheldon every now and then. Finally with an outburst of, "Ugh! I can't do this anymore! I'm gonna go for a walk!" she got up and left the room, letting the door slam shut behind her.

The boys stared at the door in shock.

"What just happened?" asked Leonard.

The others shrugged.

Penny stalked over to her apartment for a sweater and grabbed a twenty from her purse. Then she walked down the four flights of stairs and out the door leading outside. "Damn," Penny muttered to herself. "It's such a good thing I don't smoke. I'd be lighting one right now."

She walked around the block in silence, contemplating about what to do. She had to tell him. She just had to. She couldn't _not_ tell him.

"Oh my God," she groaned. "If I don't do something about this, I'm not gonna be able to sleep tonight." With an irritated groan she turned back around and made her way back to Sheldon and Leonard's apartment, but not without stopping at her own first. She took a bottle of vodka from her fridge and took a couple swallows of it.

She then walked out her door and over to the guys' apartment. She raised her hand to knock on the door. And then lowered her hand. She couldn't do it. What would she say? How would she tell him? She couldn't tell him. She turned and started back toward her room. And then turned to look back at the door; the ominous door. She groaned and walked back to the door. "Screw it," she muttered. She knocked four times and then opened the door. She popped her head in. "Sheldon, can I talk to you?"

"Okay. I don't see why not." He didn't move.

"I mean in my apartment." He still didn't move. "Alone," she tried again. "Just the two of us," she explained when he still hadn't moved.

Sheldon gave her a strange look. "I don't see why, but if you insist." He stood up and walked with Penny to her apartment.

She unlocked her door and Sheldon followed her into her apartment. "Do you want something to drink, Sheldon?"

He gave her another strange look. "Is that why you brought me here? To ask if I wanted something to drink?"

"No, Sheldon. I'm trying to be nice. I have a splitting headache and I need to go to sleep but there's something I have to tell you first because if I don't I won't be able to sleep."

She would have kept going and told Sheldon what was going on but a loud noise sounded outside her room.

"What the hell is that?" exclaimed Penny.

She opened the door to see what was outside her room. Sheldon went with her to the door. Their jaws dropped at the sight that met them. Leonard was standing in his doorway, Raj and Howard at his side.

"Oh. My. God," said Howard.

That just about summed up how they were all feeling at that moment.

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><p>Cliffhanger anybody? The next update won't be as fast. This is as far as the original un-edited version got. So now I'm done editing and now I'm writing. Hopefully, it turns out good. R&amp;R and I promise to do the same.<p> 


	3. Chapter 2

Chapter 2

There was a box sitting in the hall. A blue box. And not just any blue box, a _big_ blue box. A big blue police box to be precise.

The men could just stare, speechless.

A man walked out of the box. He was wearing a brown pinstriped suit with a tweed jacket over it. Upon scoping out his surroundings, he spotted Sheldon. He walked up to him. "Upsilon. There you are." And proceeded to grab his arm and drag him toward the box.

"Upsilon?" Sheldon asked, panic rising in his voice. "Unhand me sir. My name is Sheldon Cooper. I know not of this Upsilon fellow of whom you speak."

The Doctor stopped upon hearing these words and dropped Sheldon's arm. He looked straight at Penny. "You haven't told him yet, I take it."

"Told him what?" she asked.

"You know what."

"Penny, what is he talking about?" asked Leonard.

"He's referring to the conversation I had with my twin sister earlier." She looked back at the Doctor. "I think." She rubbed her temples. She still had a major headache.

"Care to clue us in?" he asked.

"Fine." She led everyone into her apartment. "But before I begin, I need aspirin. I have a splitting headache." She walked into her bathroom, leaving the men in her living room.

"This is impossible," laughed Howard. "You're a TV show character," he pointed out.

"Ah yes. Be that as it may, I am very much real. An old companion of mine thought it would be a hit to write about my travels and my adventures. They sold the rights to BBC and it was, as they said, 'a hit'. Which is quite unfortunate in many aspects because it makes it very difficult to fend off aliens now when everybody wants my autograph. People don't seem to realize that the fact that I'm real, makes the monsters and aliens I fight in the series very real as well."

"I'm back. I've had my aspirin. Let me explain everything. Sheldon, you might want to sit on the couch. It's quite comfortable and you might need comforting after what I'm about to tell you," she said, trying to be gentle.

"What do you want to tell me?" he asked, panic, again making his voice raise an octave.

"How do I begin? Oh wow. I don't want you guys to freak out. How about I start with the basics. Are you familiar with Wicca?" she asked.

To which the guys just looked at each other.

"Okay…Wicca. White witches."

"Like from Narnia?" asked Sheldon, still freaking out. He didn't like where this was going.

"Oh, no, no, no, honey," she said. She sat down on the arm of the couch next to him and started stroking his arm. "No, not like Jadis. White witches make white magic, good magic, as opposed to black magic. Those are called warlocks."

"Like Voldemort?" he sniffed.

Penny nodded slowly. "Yes, like Voldemort." She looked over at Leonard. "My twin sister is a witch. That's why she moved out of Nebraska to live with our aunt and uncle and Christie. My aunt, my mom's sister, was a witch. As was her husband, my uncle. My mom isn't very tolerant when it comes to witch craft. My mom and my aunt haven't spoken to each other since Billie and I were born. They only talked briefly to sort out details about Billie and send her out to live with my aunt and uncle." She took a deep breath. "Now my sister lives in San Francisco with three other witches. The three witches are sisters, the strongest witches since Melinda Warren. They are called the Power of Three, the Charmed Ones."

"Okay." Leonard drew the word a bit, sounding skeptical. He was beginning to feel uncomfortable and he didn't want to believe that this was real, but every time he chose not to believe it, his eyes trailed back to the 10th Doctor who was sitting in the chair by the island in Penny's kitchenette. "But what does that have to do with us?"

"Well, they each have a magical power. Prue was telekinetic and had the power of astral projection, but she died. Paige took Prue's place in the Sisterhood. She is part Whitelighter—which is like a guardian angel for witches. She has the power to heal which is one of her Whitelighter powers. She also has the power to orb things to her and use telekinesis. Piper has the power to freeze people or demons and make the demons explode. Phoebe has the power of empathy and premonition.

"She and Billie were in the attic going through the Book of Shadows—a witch's book of spells—and they brushed hands and Phoebe had a premonition of demons coming through the ceiling of your room. She saw me in the room and thought I was Billie. Billie was confused and then realized it must have been me she saw. So she called me to ask me if anybody new has moved into the building. She wanted to warn me."

"Is that it?" asked Leonard. "You've been acting pretty weird since that phone call. Are you sure there isn't more?"

"Nope. No more. But didn't you hear me? My twin sister is a witch and demons might be moving into the building."

"Demons?" Sheldon jumped up out of his spot in a manner that would have suggested Penny sneezed on him. "But there's no such thing as demons," said Sheldon in that tone he speaks in when he's telling someone "That's my room. People don't go in my room." He was also twitching.

"The Doctor is sitting in my living room," Penny gestured to the Doctor who waved back, "the TARDIS is sitting in the hall-way," she gestured to her closed door, "I just told you my twin sister is a witch, and you want to argue that there is no such thing as _demons_, Sheldon?" she questioned.

"Yes."

The Doctor stood up. "Fob watch. He'll be more open minded when we get him his fob watch." He walked over to Sheldon. "Where is your fob watch?"

"I'm sorry. I have no idea what you're talking about."

"Wait. Wait, wait, wait." Leonard stood up. "Are you telling us that Sheldon is Time Lord?" he asked incredulously.

The Doctor bit his lip, for once at a loss of what to say. "Of sorts," he said, choosing his words carefully.

"Well, what does that mean?" asked Howard.

"If he _is_ Upsilon, it means he is _part_ Time Lord."

"And again," Howard reiterated. "What does that mean?"

"It means we have to call up Sheldon's mom. You see, Upsilon was just a boy when he left Gallifrey. That means he's been here for a long time. He must have given his fob watch to his mom when he was a young boy."

"Oh…kay. I'll call his mom right now," said Leonard, taking his phone out of his pocket. He found Mrs. Cooper's number in his phone and hit the send button.

"Hello?" she answered.

"Hi Mrs. Cooper."

"Oh, hello, Leonard. How's Shelly? He is okay, right?"

"He's fine. He's good. But I do have a question. Does Sheldon have a fob watch there?"

"Oh dear." Mrs. Cooper collapsed into a kitchen chair. "I knew this was gonna be coming soon. Why don't you boys come down to the house and we'll look for it."

"Okay. Thank you, Mrs. Cooper." Leonard hung up his phone and looked at the Doctor. "Yep, she has the watch at the house. She wants us to go there and help her look for it."

"Alright then. Allons-y!"

Everybody walked into the TARDIS.

"Wow," exclaimed Penny. She walked back out of it and examined the outside and then stepped back in.

"This is amazing," awed Howard.

"You might want to find something to hold onto. She's a little bumpy on take-off," the Doctor warned.

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><p>The TARDIS landed outside Sheldon's house in Texas.<p>

"Oh my! What is that terrible racket?" Mrs. Cooper asked as she stepped out of her house. "Oh, what is this?" she asked.

"Hi Mom," said Sheldon once he stepped out of the blue box.

"Shelly, what is this?"

"It's called a TARDIS: Time and Relative Dimensions in Space."

She just looked at him.

"That means it's bigger on the inside than it is on the outside. It can move through time and space. It's a time machine and a teleportation device in one."

"Why don't you kids come inside? We can talk there."

Everybody sat in the living room, either on a chair or the couch or sat on the floor.

"I should start at the beginning," began Mrs. Cooper.

"I should hope you would start at the beginning. It would be useless for you to start at the end and work your way back to the beginning," complained Sheldon.

His mother gave him a stern look. "Don't you sass me, boy."

"Yes, Mommy," he sighed, leaning back in the chair.

"It was a dark night. I remember hearing screaming and hollering. I immediately ran outside to see what all the commotion was about. A young boy who looked about eight years old was running through the neighbor's yard. He looked terrified and scared out of his wits. He was also very dirty and muddy, like he had run through the ponds that are in between Beach Drive and Apffel Park Road. I took him into my house and let him wash up and calm down. Once I thought he had calmed down enough, I asked him what happened. But he didn't remember. He couldn't tell me his name or where he was from. He couldn't remember how he had gotten here, besides running. He didn't know anything about himself. He couldn't remember his parents or his family. The only personal item he had on him was a gold fob watch. I couldn't understand why anybody would give such a valuable piece of jewelry to an eight-year-old.

"The next day I took him to the police station to see if there were any missing person's on him. He stayed with me for the few weeks it took for them to find any or receive any and nothing came in. I was legally able to adopt him as my own and I did.

"I'm glad I did too. It was such a joy raising you, Shelly. You may have been hard to handle at times, but life would have been such a bore without you around."

"I love you too, Mommy."

"Do you still have the fob watch?" asked the Doctor.

"I do. I have it set aside. It was going to be Shelly's wedding present, but it seems Judgment Day has come first. Let me go get it."

"We'll come with you," said Leonard, getting up from his spot on the floor. Howard got up and followed him. Raj, not quite sure what to do, hung back and stayed on the couch. Sheldon stayed where he was in his chair. And Penny looked around nervously. She still hadn't told Sheldon he was going to die on a Friday.

She started to get up and follow Howard and Leonard when the Doctor grabbed her arm. She turned around, startled.

"We need to talk, you and I," he said.

She looked a bit scared. Did he know something?

"Let's go outside," he said, dropping her arm and walking toward the door.

She stared at his back for a second and then stood up and followed him to the door, which he held open for her.

The Doctor closed the door and turned to Penny. "There's still something you haven't told him. Why haven't you?"

"That he's going to die? I can't tell him that. He's Sheldon. That would upset him and then he'd just clam up in his room. He'd probably take the loom up again or buy another group of cats."

"A clowder," he corrected off-handedly.

"What?"

"A clowder. It's what you would call a group of cats."

"Sorry. Another _clowder_ of cats. The point is, Sheldon is a very sensitive life-form no matter how annoying he is at times. You tell him he is going to die on Chinese food night and he is not going to know how to take it. That means every Friday night he is going to retreat to his room."

The Doctor opened his mouth to speak but Penny continued.

"Now, I know. Any rational person would assume move dinner plans to someone else's house. But not Sheldon. He is a creature of habit. If the tinniest detail is out of place, he will not rest—and will not let anybody else rest—until it is resolved. You tell him he is going to die on a Friday, that is going to be all he talks about every Friday."

"Oh, I see. I have an idea. We wait until he opens the watch, and then we tell him then. Does that sound like a good plan, Billie?" he asked.

"I'm sorry, what?"

"You're Billie, aren't you?"

"Wrong sister. I'm Penny."

The Doctor laughed. "Of course you are. You have more patience than your sister does. Billie would have turned Sheldon into a preying mantis by now."

"You know my sister?"

"She was one of my companions for a bit. Only for a week. She needed a break from demons and I needed a date for a royal ball." The Doctor looked up into the sky, at the stars that weren't visible because of the daylight. He looked distant, lost in thought. "My first date choice was lost in an alternate dimension. I have no hope of getting her back, lest I open a hole in the fabric of space-time and the whole of reality comes unraveled. Then I would have destroyed so much more than just my home planet."

"Are you okay, Doctor?" asked Penny. "You seem to be rambling."

He looked at her, a blank, distant look in his eyes. He blinked and that look was gone. It was so fast she wondered if she hadn't imagined it. "Oh, I'm fine. Let's get back inside though."

"Wait, Doctor," Penny said, grabbing his jacket sleeve. "I have an idea." She whispered her idea in his ear and a grin slid onto his face.

"I like it. Very stylish. I couldn't tell you apart. What's to say the demons would be able to?"

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><p>Yay! More cliff-hangers. And yes, the Doctor knows Billie. Somehow it made perfect sense to me that between all the demon-fighting and innocent-saving the sisters do and all the earth-saving time-traveling the Doctor does, that somewhere on their journeys, they crossed paths. Perhaps a few times if not more.<p>

Review please. I will review a story of yours too. A story of your choice if you would like. I just really need feedback. Like it? Dislike it? Tell me, please.


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